1. Field of the Invention
The present invention relates to a drive device which can record and playback information into and from a recording tape, and a recording tape cartridge is mounted in the drive device. The recording tape cartridge accommodating, within a case, a single reel on which is wound a recording tape, such as a magnetic tape, which is used as a recording/playback medium mainly for computers or the like.
2. Description of the Related Art
Conventionally, recording tape cartridges (e.g., magnetic tape cartridge) have been known in which a magnetic tape, which is used as a data recording/playback medium for a computer or the like, is wound on a single reel, and the reel is accommodated in a synthetic resin case. The recording tape cartridges include a braking mechanism which prevents the reel from rotating in the case when the recording tape cartridge is not used.
That is, as shown in FIG. 10, a single reel 160 is accommodated in a recording tape cartridge 150. The reel 160 is provided with a reel hub 162, which is formed in a bottomed cylindrical shape, and whose outer peripheral portion is wound therearound a magnetic tape T. A reel gear 170 is carved in an annular form on a lower surface (outer side) of a bottom portion 168 of the reel hub 162. The reel gear 170 can mesh with a drive gear 202 formed on a rotating shaft 200 of the drive device. An engaging gear 176 is carved in an annular form on an upper surface (inner side) of the bottom portion 168. A through hole 168A is formed in an axial central portion of the bottom portion 168. An annular reel plate 172 is fixed on the lower surface of the bottom 168 radially inward of the reel gear 170. The reel plate 172 is made of magnetic material, and is provided with a hole 172A, which substantially corresponds to the through hole 168A, at the axial central portion thereof.
A disc-like brake member 180 is inserted into the reel hub 162. The brake member 180 is provided with an annular brake gear 186 at a lower surface thereof which can mesh with the engaging gear 176. The brake member 180 is formed of resin, and an engaging projection 184 projects from an upper surface of the brake member 180. Rotation-restraining ribs 194, which are formed to project downwardly from an inner surface of the upper case 152, are inserted within an engaging projection 184, which stand erect at an upper surface of the brake gear 180. In this way, the reel 160 can not rotate with respect to the case but can move vertically. A releasing projection 188 projecting from an axial central portion of a lower surface of the brake member 180 enters into a through hole 168A of the reel hub 162 and faces a gear opening 156 provided in a central portion of the lower case 154.
A compression coil spring 190 is disposed between the upper case 152 and the brake member 180. One end of the compression coil spring 190 abuts against an inner side of an annular projection 192 projecting from the upper case 152. The other end of the compression coil spring 190 abuts against an annular groove 182 formed in an upper surface of the brake member 180. In this way, usually the brake member 180 is urged downwardly by an urging force of the compression coil spring 190, and the brake gear 186 meshes with the engaging gear 176. Thus, when the recording tape cartridge 150 is not used (e.g., when it is not mounted in the drive device), the recording tape cartridge 150 is brought into a rotation-locking state in which the reel 160 is prevented from rotating with respect to the case. The reel 160 is pushed toward to the lower case 154 side by the urging force, and the reel gear 170 is exposed from the gear opening 156.
A releasing ball 204 which engages with the releasing projection 188 of the recording tape cartridge 150 is provided on an axial central portion of the rotating shaft 200 of the drive device. The releasing ball 204 is formed of metal, and is rotatably provided in a recess 208A formed in an upper portion of a holder 208 formed of resin material. A bottom surface in the recess 208A rises upward and the releasing ball 204 is projected by a predetermined height (see U.S. Pat. No. 6,452,747, for example).
Therefore, when the recording tape cartridge 150 is loaded into the drive device, accompanying the movement of the drive gear 202 to mesh with the reel gear 170, the releasing ball 204 provided on the axial central portion of the rotating shaft 200 abuts the recess 188A formed in the releasing projection 188 of the brake member 180 and pushes the same. In this way, the brake member 180 is pushed upwardly against the urging force of the compression coil spring 190, and the engagement between the brake gear 186 and the engaging gear 176 is released.
In a state where the drive gear 202 and the reel gear 170 completely mesh with each other, the reel plate 172 is attracted by a magnetic force of the annular magnet 206 provided between the drive gear 202 and the releasing ball 204. In this way, the reel 160 maintains meshing with the rotating shaft 200 and can rotate within the case. That is, when the rotating shaft 200 rotates about the axis thereof, the reel 160 integrally rotates with the rotating shaft 200.
However, at that time, since the brake member 180 can not rotate with respect to the case, the recess 188A of the releasing projection 188, the releasing ball 204 and the recess 208A (especially bottom surface) of the holder 208 slidingly contact one another. Therefore, when the rotation speed is increased to high speed or the time of which the reel 160 rotates continuously is increased, the recess 188A and the recess 208A (especially bottom surface) are worn, and there is an adverse possibility that heights of the recess 188A, the releasing ball 204 and the recess 208A are varied. Further, when the holder 208 is assembled to the rotating shaft 200, there is an adverse possibility that the height of the holder 208 (projecting height of the releasing ball 204) is varied due to forming error or the like (i.e., there is an adverse possibility that variation is caused in products).
If such varieties in heights occurs, the reel 160 can not rotate. That is, if the recess 188A and the recess 208A are worn and the releasing stroke is reduced (if the projecting height of the releasing ball 204 from the recess 208A is reduced), the brake member 180 can not be sufficiently pushed upward to the releasing position. Thus, the reel 160 can not rotate, and if the height of the holder 208 (projecting height of the releasing ball 204) is increased, the reel gear 170 and the drive gear 202 can not sufficiently mesh with each other, and thus the reel 160 can not rotate.